Wave type linear motion mechanisms are known for use as linear actuators. Wave type linear motion mechanisms comprise a circular nut made of a rigid member, a flexible screw made of a flexible member that is capable of deforming in a radial direction, and a wave generator that causes the flexible screw to deform in the radial direction and partially engage with the circular nut. The flexible screw and the circular nut have different leads. When the wave generator is caused to rotate, the engagement positions move in a circumferential direction, and relative linear movement in the axial direction is generated therebetween. If either the nut or the screw is immobilized, the other will move linearly in the axial direction. Wave type linear motion mechanisms configured as described above are disclosed in patent references 1 and 2.    [Patent reference 1] Japanese Examined Utility Model Publication 6-38195    [Patent reference 2] JP-A 2007-154955